1. Field of the Invention
The present invention relates to a servo writing in a disk drive, and more particularly, to a method, medium, and apparatus for offline self servo writing, and a disk drive using the method, capable of speedily and accurately writing servo information on a disk of the disk drive by using a reference disk assembled in an offline manner.
2. Description of the Related Art
A conventional method of writing servo information on a disk of a hard disk drive utilizes a highly accurate encoder and a mechanical pushpin. The mechanical pushpin is attached to a master actuator arm at one end and extends into the hard disk drive through a servo write slot at the other end. The master actuator arm is operated under a closed loop by using a positioner and the highly accurate encoder. In addition, a clock head is directed to write a clock track onto the disk to serve as a timing reference during a servo writing process. This servo writing process suffers from problems associated with non-repetitive run-out (NRRO), disk flutter, and motor rocking, all of which cause degradation of accuracy of position information written during the servo writing process. Moreover, the use of the positioner and encoder greatly increases expenses associated with the servo writing process and reduces productivity.
In order to solve these problems, an offline servo writing method and a self servo writing method have been developed.
In the offline servo writing method, each disk is servo-written by using an offline servo track writer before being installed into a hard disk drive assembly. While this method has the benefit of increased accuracy, it also has problems of increased repeatable run-out (RRO), due to shifting of a center of a disk, and a strict requirement for an additional track checking process at the time of head conversion.
On the other hand, a self servo writing method is a method of writing servo information by tracing pre-written reference servo information. In this method, the quality of written servo information is dependent on the accuracy of the reference servo information. The self servo writing method has the advantage of being inexpensive in implementation because of not having to greatly depend on a servo writer. However, it also suffers from the disadvantage of increased self servo writing time and deteriorated capability in following the reference servo information.
In order to solve these problems, a new servo writing method has been disclosed in U.S. Pat. No. 6,411,459. In this method, a reference disk and several blank disks are assembled in a disk drive, and servo information is then written on the blank disks by using the reference disk.
However, as shown in FIG. 1, in this conventional method, a track width in a servo pattern of the reference disk is larger than that in a final servo pattern of a copied disk. If there are irreparable defects in some portion of the reference servo pattern of the reference disk, the defects actually affect several tracks in the copied disk. For example, when three servo tracks are copied from a single servo track of the reference disk, an error in a single burst signal of the servo pattern of the reference disk -will prevent copying of the three servo tracks. In addition, the required time for copying servo information increases and stability of servo pattern tracing becomes deteriorated.